This invention relates to a communication system and, more particularly, to a communication system which is adapted to reduce the effect of reverberations upon the quality of signal transmission.
Certain environments are known to produce reverberation on signal transmission paths. For example radio frequency transmission of signals in a mountainous region experience reflections from the mountains with resulting multipath communication of the signals between a point of transmission of the signals and a point of reception of the signals. Slight variations in the lengths of propagation paths, as may be induced by perturbations in the atmosphere, result in a composite signal at the point of reception which tends to fade in amplitude as the phases of the signals on the various propagation paths vary with respect to each other. A similar, but more intense, situation exists in underwater communication in which sonic energy reflects off surfaces of submerged objects, refracts off thermoclines, and is selectively absorbed in some media such as the ocean bottom. The length of sonic vibrations in an underwater environment are often so long as to have precluded all but the slowest rates of communication.
In the past, attempts have been made to negate the effects of reverberation by multiple tone signaling at very slow data rates, these data rates being slower than the signal fading rate. By means of the multiple tone or multiple channel signaling systems, increased data rates have been obtained at a cost of an increased number of channels. However, heretofore it has not been possible to obtain a data rate, which is higher than the signal fading rate by means of a single tone or single channel system.